Industrial controllers have been used for many years in industrial control applications. The advent of the industrial controller allowed the replacement of electromechanical relay panels, used for on-off sequencing of industrial devices, by solid-state power modules. Today, the industrial controller has evolved to include capabilities to perform data acquisition and storage, to execute complex mathematical algorithms, and to perform system troubleshooting, to name a few.
The industrial controller is programmed by storing instructions into an internal memory circuit. Some controllers are programmed by entering the instructions using a keyboard on a control panel. Many modern controllers are programmed using a host computer equipped with a suitable software package. Using the suitable software, high-level instructions are entered into the host computer and compiled to form a control program. The control program is transferred to the controller either by a communication link between the controller and the computer, or by storing the control program in a non-volatile memory for physical transfer to the controller.
Some current systems use the host computer for accepting instructions in a high-level language for compilation into the control program for transfer to the controller. Other systems accept instructions in a ladder-based language for compilation into the control program. Further, some systems convert instructions in the ladder-based language to corresponding instructions in the high-level language so that the high-level language instructions can be compiled to form the control program.